How do i permanently embed subtitles in the movie so that i can watch them on my ipod..freeware..any..?

i have movies on my pc..i can get the subtitles with the movie while watching on my pc..after downloading them and putting them in the same folder in which the movie file is..only prob is..i wanna watch them on my ipod..how can i permanently embed those subtitles in the movie itself..please suggest something..i have been searching a lot but got upto nothing..i want any app, if there is, for free..that can do this..thanx